| Summary: | 碩士 === 國防大學中正理工學院 === 應用化學研究所 === 94 === In this work, fine powders of SrFe12O19 with different contents of SrTiO3 additive (SrFe12O19+xSrTiO3, x=0.00, 0.05, 0.10, 0.15 and 0.20, respectively) were successfully prepared via a quasi-dry combustion synthesis route using Sr(NO3)2, Fe(NO3)3．9H2O, glycine (NH2CH2COOH) and Ti powder as reactants. By directly mixing and thoroughly dehydrating, a flammable dried mixture with good homogeneity can be obtained. Once ignited in the air at room temperature, it underwent a combustion process, and with a large amount of gas smoke, a voluminous loose product was yielded. The as-synthesized powder was calcined at various temperatures, up to 1200 ℃, to study the effects of calcination temperature on phase development and products’ properties. The resultant powders were characterized by X-ray diffractometry, infrared (IR) spectrometer, simultaneous thermalgravity (TG)-differential scanning calorimetry (DSC)-mass spectrometry (MS) analysis, scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and measurement of surface area. When x=0.00 was used, a nearly pure SrFe12O19 product was obtained at temperatures as low as 1000 ℃. Pure single-magnetic-domain SrFe12O19 powders with the crystalline size ranging from ~60 to 75 nm could be observed at 1050 ℃, which exhibited an maximum intrinsic coercivity (iHc) of 5.95 kOe, the attained magnetization value (Mmax, measured at 15kOe) of 60.13 emu/g as well as the residual magnetization (Mr) of 31.75 emu/g. Whereas, upon calcining at 1200 ℃, the Mmax increased further, to 68.52 emu/g; but the iHc value reduced. According to the experimental results obtained, a possible mechanism for the formation of strontium ferrite is proposed. The as-synthesized powders and the calcined ones, obtained using different x values, were introduced into polyurethane matrix to prepare a testing specimen. The relative complex permittivity ( ) and permeability ( ) of the composite materials were measured in the frequency range of 1-12 GHz by using a network analyzer. When the amount of SrTiO3 additive incorporated into SrFe12O19 varied from 0 to 20 mol%, not only improved the as expected, but also modified the . The effect of calcination temperature on the values of and was similar to that of amount of SrTiO3 additive. The influences of both the calcinations temperature and amount of SrTiO3 additive were explained judging from the results of observations of products’ morphology, XRD analysis of phase component and measurements of magnetic properties.
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